Muller is credited with coining the term “telomere.” The work of Barbara McClintock demonstrated that broken chromosomes have sticky ends when compared to natural chromosomal ends, which are stable and do not have a tendency to fuse together. Telomeres are responsible for preventing chromosomes from adhering to one another and for protecting them from deterioration.
Telomeres include non-coding repetitive sequences that are abundant in Guanine nucleotides, which are essential for cell survival. It is 5′-TTAGGG-3′ that is repeated repeatedly in humans, and it is replicated several times in other animals.
Incomplete replication at the end of the chromosomes results in the formation of telomeric sequences (telomeres). Each time the DNA is replicated, a portion of the DNA is lost. By using protective end caps, we can ensure that genetic information is not lost during the manufacturing process.
They play an important part in the process of aging.
Structure of the Telomere
Telomeres are found at the ends of chromosomes in all eukaryotic organisms, except for bacteria. It is made up of small nucleotide sequences that are repeated many times during the course of the genome. They do not contain any protein-coding sequences.
The sequence that is repeated varies from one species to another in different environments. The number of copies of the repeating units varies from chromosome to chromosome, and even within the same chromosomes of different cells, depending on the cell type being studied. In normal somatic cells of humans, approximately 500 to 3000 repeats are present, with the length of each repeat decreasing gradually. Telomeres do not shorten in some cells, such as germ line cells and cancerous cells, as a result of the passage of time.
In most species, the basic pattern of the repeating unit is 5’-T1-4A0-1G1-8-3’, with the exception of a few that have a different pattern. Telomeres are characterised by the presence of guanine-rich single strands at the 3′ end. In humans, t-loops are created at the end of single strands that are 3′ in length. Protection against telomere degradation or alteration is provided by the protein Shelterin.
Humans have a repetitive pattern that is 5′-TTAGGG-3′ in length. TTTAGGG is the genetic code for the plant Arabidopsis thaliana. Additional sequences related with telomeres are present in the majority of the species studied.
Terrestrial vertebrates have a high frequency of telomeres with the tandem repeats TTAGGG. Among the more than one hundred species that have been identified thus far are birds, reptiles, amphibians, fish, and mammals.
Because DNA in most prokaryotes is circular, telomeres are not found in these organisms. Some prokaryotes with linear DNA have telomeres, but the structure of these telomeres is different from that of eukaryotic cells. Typically, they are in the shape of a hairpin loop created by a single strand of DNA or they are coupled to proteins.
Shortening and Its Relationship to Ageing and Cancer
Telomeres serve an important part in the ageing of cells by shortening their length. Telomeres get shorter and shorter with each replication, and when they get too short, the cells stop reproducing and die, resulting in senescence and apoptosis. Therefore, it serves as a biological clock for the progression of cellular ageing. It can also result in the transformation of cells into cancerous tumours.
Effect On Ageing
The rate of telomere shortening can be slowed down by adopting a healthier lifestyle, eating better, and participating in more activities. It both prevents the onset of age-related disorders and enhances the length of one’s life.
A unique enzyme known as ‘Telomerase’ has the ability to lengthen the length of telomeres in cells. It can be found in cells that have the ability to divide indefinitely, such as unicellular eukaryotes, egg and sperm cells, blood cells, and cancer cells, among other things.
Effect on Cancer
Scientists have discovered that cancer cells have telomeres that are too short, and that when this occurs, telomerase is reactivated, causing cancer cells to multiply in an uncontrolled manner. The majority of cancer cells, such as those found in the breast, prostate, lung, pancreas, and other organs, have telomerase, which helps to maintain telomere length and prevent apoptosis. The development of an anti-cancer medication that targets telomerase is now underway.
As a result, telomeres are critical in the preservation of genes on DNA and the slowing of cellular ageing. It protects the genome from degradation, unneeded repair and recombination, as well as fusion of two chromosomes, among other things.
Conclusion
When the centromere is placed at the terminal end of the chromosome, it is known as a telocentric chromosome. Telocentric chromosomes are distinguished by their shape, which is similar to the letter I.These chromosomes include a nucleotide sequence that is repeated at either end of the chromosomes.Cell division is prevented from deteriorating or fusing the ends of the chromosomes with those of their neighbours by the presence of the nuclear envelope (nucleus).